This invention relates to an electrode used for a generating channel in the magnetohydrodynamic (MHD) power generator.
The generating channel comprises an electrode wall formed of a multiplicity of electrode modules disposed neatly side by side and an insulating wall formed by disposing a multiplicity of electrical insulation modules neatly side by side. The interior of the generating channel is exposed to a high-temperature combustion gas plasma containing a seed agent and flowing at a very high speed under a high magnetic field. Of the component elements of the generating channel, the electrode wall has direct bearing upon the electric current. The electric characteristics of the electrode wall, therefore, require careful consideration. The service life of the generating channel is governed by the susceptibility of the electrode wall to deterioration and damage. Generally the damage done to the electrode by the electric current is chiefly ascribable to the heat generated by localized distribution of the electric current in the surface region of the electrode. This phenomenon of electric current concentration is closely related to current density and flux density. The tendency toward electric current concentration grows with the decreasing surface temperature of the electrode. When a strong magnetic field of about 5 Teslas (Wb/m.sup.2) acts upon an electrode having an average current density of about 1 A/cm.sup.2, for example, concentration of electric current occurs in the upstream portion of the anode or in the downstream portion of the cathode. In such a portion, the maximum current density rises above 2 A/cm.sup.2. Under the condition of such a high current density, an arc is produced on the cathode side and abnormally localized heat is generated there to vaporize part of the electrode. On the anode side, the heat similarly generated affects the upstream portion of the electrode and causes this portion to be deteriorated and worn out as by oxidation or a chemical reaction. As described, the wear of the electrodes due to the concentration of electric current selectively occurs in terminal portions of the electrodes. The service life of the electrode wall, accordingly, is determined by the speed at which the wear proceeds in such terminal portions. For the service life of the generating channel to be prevented from being shortened by the local wear of the electrode, it is necessary that the distribution of electric current in the surface region of the electrode should be uniformized so as to average the distribution of the wear of the electrode. Realization of this requirement can be expected to ensure a notable elongation of the service life of the electrode wall. Thus, an acute need has been felt for the development of electrode design and material which provide required uniformization of the distribution of electric current in the electrode.
Recently there has been proposed a construction such that the uniformization of electric current on the electrode is promoted by distributing the surface temperature of the electrode in the direction of the flow of the combustion gas, selectively setting the surface temperature of the portion of the electrode not liable to concentration of electric current at a higher level than in the other portion thereby facilitating the reception of electric current in the selected portion, and consequently lowering the current density in the portion liable to concentration of electric current (AIAA Journal, Vol. 15 No. 1, Jan. 1976, pp 116-117). With this construction, however, the uniformization of the distribution of electric current is obtained only to a limited extent. Moreover, good matching between the distribution of electric current and that of surface temperature can be obtained only by a complicated process of trial and error.